The present invention relates generally to an exposure apparatus and a method used to fabricate various devices including semiconductor chips such as ICs and LSIs, display devices such as liquid crystal panels, sensing devices such as magnetic heads, and image pick-up devices such as CCDs, as well as fine patterns used for micromechanics, and more particularly to an immersion type exposure method and apparatus that immerse the final surface of the projection optical system and the surface of the object in the fluid and expose the object through the fluid.
A projection exposure apparatus has been conventionally used to transfer a circuit pattern on a reticle (or a mask) via a projection optical system onto a wafer etc. and high-quality exposure at a high resolution has recently been increasingly demanded. The immersion exposure has attracted attention as one means to meet this demand. The immersion exposure promotes a higher numerical aperture (“NA”) by replacing a medium (typically air) at the wafer side of the projection exposure with a fluid. The projection exposure apparatus has an NA=n·sin θ where n is a refractive index of the medium, and the NA increases when the medium has a refractive index higher than the air's refractive index, i.e., n>1.
For the immersion exposure, some methods have already been proposed which fill the fluid between the object to be exposed, and the optical element in the projection optical system that is closest to the object. See, for example, International Publication No. WO99/49504, and International Symposium on 157 nm Lithography, 3-6 Sep. 2002, Belgium, Bruce Smith et al. (Rochester Institute of Technology), Extreme-NA Wafer Immersion Lithography for 35-65 nm Technology. These prior art references propose to provide, as shown in FIG. 9, a supply nozzle 18 and a recovery nozzle 20 near a final lens 14 in the projection optical system, and to supply fluid 16 from the supply nozzle 18 between the substrate W and the final lens 14. In addition, an air curtain is formed by blowing compressed air to the outside of the fluid 16 and maintaining the fluid 16 between the substrate W and the final lens 14. Here, FIG. 9 is a schematic sectional view for explaining the fluid supply and recovery by a conventional immersion type exposure apparatus. Upon introduction of the fluid 16, an interval between the substrate W and the final lens 14 is maintained to be a necessary interval for exposure, and the exposure becomes immediately ready after the introduction. The exposure is performed, while the supply nozzle 18 continuously supplies the fluid 16 and the recovery nozzle 20 continuously recovers the fluid 16 or while the fluid 16 circulates between the substrate W and the final lens 14.
However, the conventional immersion exposure shown in FIG. 9 causes, when the end of the substrate W is located inside of the outer edge of the supply nozzle 18, dropping of the fluid 16 supplied from the supply nozzle 18. Since the recovery nozzle 20 collects the fluid 16, no fluid 16 exists between the final lens 14 and the substrate W, or at least air bubbles mix. The air bubbles shield the exposure light, resulting in lowered transfer accuracy and yield, so that the demand for the high-quality exposure cannot be satisfied. The air bubbles cannot be eliminated even when the fluid 16 is supplied and recovered continuously.
Even when there is fluid between the substrate W and the final lens 14 as a result of the initial filling, etc., if the surface of this fluid is spaced from the surface of the fluid supplied from the supply nozzle 18, the contact of these surfaces of the fluids by the continuous supply of the fluid from the supply nozzle 18 is likely to generate air bubbles.